One-Time Colon Exam Yields Big Benefits

Action Points

Explain to patients that a limited examination of the colon (by flexible sigmoidoscopy) reduced the incidence of colorectal cancer and colon-cancer mortality compared with no screening.

Note that the study was conducted in England, where the approach to colorectal cancer screening differs from that of the U.S., particularly with respect to use of colonoscopy.

A single sigmoidoscopy study in middle age reduced colorectal cancer mortality by more than 40% and incidence by one-third, data from a large, randomized clinical trial in the U.K. showed.

Patients assigned to this limited examination of the colon had a 50% reduction in cancer of the distal colon, compared with a control group that did not have sigmoidoscopy.

Flexible sigmoidoscopy also was associated with a trend toward lower overall mortality, and the results suggested the one-time procedure would save money by reducing the incidence of colon cancer and associated treatment costs, investigators reported online in The Lancet.

"There's never been trial evidence that removing polyps prevents cancer," Wendy S. Atkin, PhD, of Imperial College London, said at a news conference to announce the results. "There has been lots of indirect evidence, but there has never been a trial."

"A once-only examination gives a very big effect over the whole of the bowel, including that it isn't even examined," she added.

U.S. specialists, who generally prefer more extensive, and expensive, colonoscopy -- gave the study mixed reviews. But they agreed that it provides ammunition for the overall benefits of colorectal cancer screening.

"This is an extremely significant study which clearly shows, within the context of a randomized clinical trial, that endoscopic screening leading to the removal of polyps . . . will reduce colon-cancer specific mortality," Robert Mayer, MD, of Dana-Farber Cancer Institute in Boston, said in response to a query from MedPage Today and ABC News.

"Such a positive effect had been assumed for several years and is incorporated into present screening guidelines in the U.S. . . . but -- until the publication of this report -- had not been validated prospectively."

In contrast, Roshini Rajapaksa, MD, of New York University, said the results were "not that significant." Like most other American specialists contacted, she defended full colonoscopy.

"Previous studies have shown that flexible sigmoidoscopy reduced mortality from colorectal cancer. And if the study had compared sigmoidoscopy with colonoscopy, the colonoscopy patients most likely would have had a greater reduction in mortality. So colonoscopy still remains the best test for colorectal cancer screening. However, sigmoidoscopy is cheaper, and certainly better than no test at all," Rajapaksa said.

All of the specialists who responded to the query noted the most glaring limitation of sigmoidoscopy.

"The significance of this study is that it provides further evidence that colorectal cancer screening saves lives," said Fritz Francois, MD, also of New York University. "However, we know that colon polyps and cancer can occur on the side not examined by the sigmoidoscope [right colon], and therefore colonoscopy remains the much more complete gold standard able to detect and remove precancerous lesions.

"In the U.S. we have seen a shift in the distribution of colonic lesions towards the right side, and this is particularly evident in certain racial/ethnic groups. Therefore, sigmoidoscopy would not be the best option," he added.

The results came from a study involving 170,000 people ages 55 to 64, living in England, Wales, and Scotland. All of the participants responded to a questionnaire indicating their willingness to be screened for colon cancer. Subsequently, the participants were randomized 2:1 to no screening or to a one-time, flexible sigmoidoscopy procedure.

The rationale for the study came from the recognition that screening can prevent colorectal cancer by detection and removal of adenomas.

Two-thirds of colorectal cancers and adenomas arise in the rectum and sigmoid colon, where they can be identified and examined by flexible sigmoidoscopy, Atkin and co-authors wrote in The Lancet.

Most people who develop distal (left-sided) colon cancer have adenomas by age 60, the authors continued. Use of sigmoidoscopy to detect and remove adenomas affords long-term protection against distal colon cancer.

The clinical trial tested the hypothesis that a single sigmoidoscopy performed in people 55 to 64 would be a cost-effective and acceptable method to reduce colorectal cancer incidence and mortality.

Atkin and co-authors reported results from 11 years of follow-up.

During that time, 1,818 members of the control group developed colorectal cancer as did 706 in the sigmoidoscopy group. Additionally, 538 patients in the control group died of colorectal cancer compared with 189 in intervention group.

The differences translated into a 23% reduction in the incidence of colorectal cancer (HR 0.77, 95% CI 0.70 to 0.84) and a 31% reduction in colorectal cancer-specific mortality in favor of the sigmoidoscopy group (HR 0.69, 95% CI 0.59 to 0.82).

Investigators determined that 191 patients would have to be screened to prevent one colorectal cancer diagnosis and 489 to prevent one colorectal cancer death.

The results are consistent with screening guidelines of the American Cancer Society and the U.S. Preventive Services Task Force, both of which recommend sigmoidoscopy every five years as a screening option, said Durado Brooks, MD, director of prostate and colorectal cancer for the ACS.

"The American Cancer Society sees this trial as significant," Brooks said in an interview. "Its findings support our current guidelines that include flexible sigmoidoscopy as one of several options. Perhaps most important is the study's reinforcement that the benefits of colorectal screening are not in doubt."

A clinical spokesperson for the American Society of Clinical Oncology agreed with Brooks that the trial proves that screening prevents cancer and saves lives. However, the trial left several issues unresolved.

"I don't think it applies to our guidelines because it doesn't compare [sigmoidoscopy] to colonoscopy, and it doesn't tell us whether one examination is better than examinations over time at a longer interval, Jennifer Obel, MD, of NorthShore Health System in Chicago, said in an interview.

"The trial validates that we can prevent colon cancer, and I think that's the take-home message of this study, she added.

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